By Italian law dried pasta must be made with 100% durum semolina flour and water.Dried pasta, especially the more complex shapes (such as radiatore) are designed for grabbing and holding onto sauces. Dried tube pasta (ziti or penne) often has ridges or slight abrasions on the surface as well. These ridges and bumps are created during the extrusion process, when the pasta is forced from a copper mold and cut to desired length before drying. These molds, while expensive and prone to wear are favored for making the best dried pasta. However most producers worldwide use steel molds that produce pasta that is too smooth.